A Minor Isoform of the Human RNA Polymerase II Subunit hRPB11 (POLR2J) Interacts with Several Components of the Translation Initiation Factor eIF3

Using the yeast two-hybrid (YTH) system we have uncovered interaction of the hRPB11c alpha minor isoform of Homo sapiens RNA polymerase II hRPB11 (POLR2J) subunit with three different subunits of the human translation initiation factor eIF3 (hEIF3): eIF3a, eIF3i, and eIF3m. One variant of eIF3m identified in the study is the product of translation of alternatively spliced mRNA. We have named a novel isoform of this subunit eIF3m beta. By means of the YTH system we also have shown that the new eIF3m beta isoform interacts with the eIF3a subunit. Whereas previously described subunit eIF3m alpha (GA17) has clear cytoplasmic localization, the novel eIF3m beta isoform is detected predominantly in the cell nucleus. The discovered interactions of the hRPB11c alpha isoform with several hEIF3 subunits demonstrate a new type coordination between transcription and the following (downstream) stages of gene expression (such as mRNA transport from nucleus to the active ribosomes in cytoplasm) in Homo sapiens and point out the possibility of existence of nuclear hEIF3 subcomplexes.